Formatt 77mm Screw-In Adapter Ring for FM500 Matte Box Glass filters are made with Schott Water White Optical glass Color and effects are digitally applied to a wafer thin mebrane layered between two pieces of ground glass. This process is called A.C.T(Absorption Cell Technology) All Formatt filters are polished to within 2 microns of optical flatness Formatt filters are 1mm thick and edge framed. All filters come with a individual wave deviation chart to certify quality. All filters come with a 10 year guarantee against fading or color shift.